Recently, the effect of ultraviolet on the skin has become widely known recently, and users have become increasingly conscious of skin whitening. Thus, there is demand for a cosmetic which provides a higher UV protection ability and even a good feeling in use.
Due to the fact that an O/W emulsified composition can provide refreshing and light fresh feeling in use while it contains oils, such emulsified composition is widely used not only in cosmetics for basic skin care such as milky lotions and creams, but also in products such as foundations and sunscreen cosmetics.
In cosmetics, UV protection ability has been often provided by incorporating organic UV absorbers or inorganic UV scatterers such as fine particle titanium oxide and fine particle zinc oxide. However, when a high UV protection ability is tried to be provided over a wide range of UV-B to UV-A by incorporating a large amount of inorganic UV shielding powder such as fine particle titanium oxide and fine particle zinc oxide, the finish may become whitish, or frictional or powdery feeling may be caused.
In contrast, many organic UV absorbers are generally highly polar oils and do not cause the problems such as the whitish finish and frictional or powdery feeling mentioned above. However, they provide stickiness so much to deteriorate the refreshing feeling of O/W emulsified composition when the emulsified composition is applied to skin. In addition, the emulsion stability tends to decrease. In particular, when octocrylene and ethylhexyl methoxycinnamate are used in combination as organic UV absorbers, an excellent UV protection ability can be achieved, but it has been difficult to obtain an O/W emulsified composition with a high emulsion stability and a good feeling in use.
Bis-ethylhexyloxyphenol methoxyphenyl triazine is a highly excellent organic UV absorber because of its UV absorbing ability in a wide range of UV-A to UV-B. However, it is essentially a crystalline solid at ordinary temperature, and there has been a problem that it precipitated over time when it was dissolved in the oil phase to prepare an O/W emulsified composition.
Methylene bis-benzotriazolyl tetramethylbutylphenol is a solid organic UV absorber which is essentially insoluble in water and oils, and it generally shows its UV protection ability by being dispersed, in the from of fine particle powder, in products such as cosmetics. Though methylene bis-benzotriazolyl tetramethylbutylphenol is a highly excellent organic UV absorber because of its UV absorbing ability in a wide range from UV-A to UV-B, it is desired to be used in combination with other UV absorbers so as to achieve higher UV protection ability.
However, when methylene bis-benzotriazolyl tetramethylbutylphenol is dispersed in the aqueous phase of an O/W emulsified composition containing, in the oil phase, octocrylene which is an organic UV absorber in an oil state at ordinary temperature, the fine particle powder of methylene bis-benzotriazolyl tetramethylbutylphenol coarsens (agglutinates) over time in water to cause a decreased UV protection ability or a rough feeling in use problematically. Also, as octocrylene is highly polar, there has been a problem that octocrylene was difficult to be emulsified stably in water, and furthermore provided significant stickiness.
Patent Literature 1 suggests that fine particles of an insoluble UV absorber, such as methylene bis-benzotriazolyl tetramethylbutylphenol is incorporated in an emulsion with use of a crosspolymer of ethylenically unsaturated monomers, without using an emulsifier to stability over time and water.
However, even such a method could not achieve sufficient feeling in use or formulation stability.
Patent Literature 2 describes an O/W emulsified composition in which fine particles of methylene bis-benzotriazolyl tetramethylbutylphenol is dispersed in the aqueous phase with, as an emulsifier, a copolymer of polyacrylic acid and alkyl acrylate, or a nonionic surfactant with HLB of 8 or more and/or a fatty acid soap.
However, it does not investigate the inhibition of coarsening or precipitation of fine particles of methylene bis-benzotriazolyl tetramethylbutylphenol in case where octocrylene is incorporated.